Method for anonymously identifying a security module

ABSTRACT

A method for anonymously identifying a security module by a server. The method includes: receiving, from the module, a request for the address of a server managing subscription data of an operator, the request including a current identification value of the module, which depends on an identifier of the module and a current date; searching for the current identification value in at least one set of identification values, the set being associated with an operator and including, for a given module, a plurality of identification values, which are calculated depending on the identifier of the module and a date, the date varying for the plurality of identification values of the set between a start date and an end date; and sending, to the security module, the address of the server managing subscription data associated with the operator when the current identification value appears in the set of identification values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Section 371 National Stage Application ofInternational Application No. PCT/FR2016/052903, filed Nov. 9, 2016, thecontent of which is incorporated herein by reference in its entirety,and published as WO 2017089672 on Jun. 1, 2017, not in English.

FIELD OF THE DISCLOSURE

The present invention relates to a method of anonymous identification ofa security module when subscribing to a telecommunications operator.

It finds a particularly beneficial application within the framework ofthe use of security modules embedded in a mass-market mobile device andmore particularly when subscribing to a mobile network operator, or whenthere is a change of operator.

BACKGROUND OF THE DISCLOSURE

The association of mobile telephone operators, or “GSMA” (standing for“Global System for Mobile Communications”) has announced the developmentof an embedded “SIM” (standing for “Subscriber Identity Module”), or“eSIM” card standard, of “eUICC” type (standing for “embedded UniversalIntegrated Circuit Card”) for mass-market mobile devices, such as amobile terminal or a tablet. An embedded SIM card is intended to beirremovable and (re)programmed remotely. Thus, when acquiring a newmobile device, it is no longer necessary to manipulate the SIM cardbeforehand in order to access an operator's network, or indeed to changeit when there is a change of operator. Provision is made for a user tosubscribe directly via the screen of his mobile device, or by going to ashop of the operator or/and for him to install an additional profile foraccessing the network on a secondary device. Provision is also made forhim to change operator in the same way. An eSIM card is identified in aunique manner by means of a module identifier or “EID” (for “eUICCIdentifier”), which constitutes a factory-defined physical identifier ofthe card. This identifier is not modifiable.

Within the framework of mass-market mobile devices, it is possible thatno initial profile for accessing a mobile network is installed in thefactory. The device therefore basically has no possibility of accessingthe radio pathway. It is conceivable, when taking out a subscription toa mobile network operator, to manage in an intermediate server of thenetwork which is independent of the operators a correspondence betweenthe identifier of the eSIM card and the operator with which thesubscription has been taken out and for which the operator has at itsdisposal an access profile that it has generated for the eSIM card.Thus, when a mobile device wishes to obtain a profile for accessing thenetwork after a subscription is taken out with an operator, it addressesitself to the intermediate server which identifies, on the basis of theidentifier of the eSIM card of the mobile device, the operator thatgenerated a profile for this device. The intermediate server thendispatches to the mobile device the address of a management server ofthe operator from which it can obtain its profile. The mobile device canthen establish a connection with the management server of the operatorin a data network such as the Internet so as to recover its profile andinstall it in the eSIM card.

Such a solution offers a certain flexibility in the management ofsubscriptions by the user who can easily control from his mobile devicethe activation of a subscription, or of a new subscription in the caseof a change of operator. However, this management poses serious problemsregarding respect of the user's private life. Indeed, the intermediateserver of the network which stores the correspondences between eSIM cardidentifier and address of a management server of the operator whichgenerated the profile for accessing the network knows at a given instantthe operator associated with an eSIM card. It is furthermore capable oftracing all the changes of subscription of the eSIM card in the courseof the life of the eSIM card.

SUMMARY

An exemplary embodiment of the invention proposes a method of anonymousidentification of a security module by a server, said method comprising:

-   -   reception from the module of a request for address of a server        for managing subscription data of an operator, said request        comprising a current identification value of the module, said        current identification value being dependent on an identifier of        the module and a current date,    -   searching for the current identification value in at least one        set of identification values, said set being associated with an        operator and comprising for a given module, a plurality of        identification values, an identification value being computed as        a function of the identifier of the module and of a date, the        date varying for the plurality of identification values of the        set between an initial date and a final date,    -   dispatching to the security module of the subscription data        management server address associated with the operator when the        current identification value figures in the set of        identification values.

With the method described here, an identification value which isassociated with the security module is decorrelated from the physicalidentifier of the module. Thus, the server of the network which receivessuch an identification value in order to identify the address of a datamanagement server to be contacted so as to obtain a profile foraccessing the network cannot identify the security module which hidesbehind the identification value. The anonymity of the security module isthus safeguarded.

Moreover, the identification value associated with a security moduleevolves over time since its computation takes into account a date. Afirst identification value, generated for a module at a first date whentaking out a subscription with a first operator and a secondidentification value, generated for the same module at a second date,when taking out for example a subscription with a second operator, aretherefore necessarily different. Thus, it is not possible for the serverto trace the successive subscriptions of a security module when there isa change of operator.

Anonymity and non-traceability contribute to the respect of the privatelife of the user who owns the mobile device which comprises the securitymodule.

Moreover, searching for the current identification value of the securitymodule in the list of identification values makes it possible to takeaccount of a period of validity of the network access profile. Indeed,if the search for the current identification value of a security modulein the list of identification values stored by the server fails,although a subscription has been taken out previously for the mobiledevice which comprises the security module, this may signify that theprofile is no longer available. A validity period is indeed associatedwith a profile for accessing the network and it is not possible toobtain the profile beyond this validity period. The currentidentification value of the module taking account of the current date,it might therefore not be present in the identification values listassociated with the security module if the current date has exceeded theperiod of validity of the profile. This avoids needless prompts to theserver for managing subscription data of an operator and specificmanagement of the period of validity of the profile.

According to an exemplary embodiment, the method comprises in a priorsubscription phase:

-   -   reception, from the server for managing the subscription data of        the operator of the set of identification values of the module,        said set being associated by the server with the operator.

When taking out a subscription with an operator from a mobile device,the subscription data management server generates a set of anonymousidentification values which are specific to the module included in thedevice which takes account of the period of validity of the profilebeyond which the profile is no longer valid. This set thus comprises theset of identification values that might be received from the securitymodule in a request for address of subscription data management serverof the operator in the guise of current identification value.

In an exemplary embodiment, the method furthermore comprises:

-   -   application of a group signature algorithm parametrized by a        secret key specific to the security module to the request for        address of the subscription data management server of the        operator,    -   verification of the signature of the request for address by the        server by means of a group public key, associated by means of a        public key certificate with a set of modules comprising at least        said security module.

The server verifies that the security module is an authentic modulewhich belongs to an identified group, for example a group of securitymodules arising from one and the same card maker. Moreover, by virtue ofthe implementation of the group signature algorithm, the server is notcapable of individually identifying the module. The security module thusauthenticates itself anonymously with the server.

In an exemplary embodiment, an identification value is computed byapplying a hash function to a date and by raising the value obtained tothe power of an identifier derived from the identifier of the module.

The computation of an identification value of the module, be its acurrent identification value or an identification value from the list ofidentification values, guarantees a high level of security. Indeed, sucha formula can be reduced to a known problem, the so-called discretelogarithm problem, presumed to be difficult to solve in a reasonabletime. Thus, to find the exponent, here EID′, knowing the hash of thedate is a difficult problem. The anonymity property of the securitymodules is thus proven mathematically. Likewise, if two values,H(d₁)^(EID1′) and H(d₂)^(EID2)′, are available, it is not possible toknow whether EID₁′=EID₂′. Solving such a problem would amount to solvingthe Diffie-Hellman decisional problem (or “DDH”, for “DecisionalDiffie-Hellman”), presumed to be difficult. Thus, the server cannotestablish any link between requests for server addresses emanating fromone and the same security module or between two lists of identificationvalues. The server may receive such requests when subscribing todifferent operators. Thus, the non-traceability property ismathematically proven.

In an exemplary embodiment, the derived identifier comprises at least160 bits. This exemplary embodiment takes account of the fact that theformat of a security module identifier can comprise fewer than 160 bits.It is estimated that 160 bits is a sufficient size to guarantee theanonymity and non-traceability properties. It is estimated thatcurrently the ideal value is 256 bits.

In an exemplary embodiment, the derived identifier is obtained byconcatenating the identifier of the module with a random value.

In an exemplary embodiment, an identification value is computed byapplying a hash function to the concatenation of a first identifierderived from the identifier of the module and of the hash of theconcatenation of a second identifier derived from the identifier of themodule and the date.

This way of computing an identification value of the module, be it acurrent identification value or an identification value from the list ofidentification values offers good performance in terms of computationtime. Indeed, the operations implemented are less complex than thosedescribed previously.

The invention also relates to a server of a network designed toanonymously identify a security module, said server comprising:

-   -   reception means, designed to receive from the module, a request        for address of a server for managing subscription data of an        operator, said request comprising a current identification value        of the module, said current identification value being dependent        on an identifier of the module and a current date,    -   search means, designed to search for the current identification        value received from the module in at least one set of        identification values, said set being associated with an        operator and comprising for a given module, a plurality of        identification values, an identification value being computed as        a function of the identifier of the module and of a date, the        date varying for the plurality of identification values of the        set between an initial date and a final date,    -   dispatching means, designed to dispatch to the security module        the address of the profiles data management server associated        with the operator when the current identification value figures        in the set of identification values.

The invention also pertains to a system for obtaining a network accessprofile, comprising:

-   -   the server such as described previously,    -   a mobile device comprising the security module, said device        being designed to dispatch to the server a request for address        of a server for managing the subscription data of the operator,        to receive in response the address of said management server,        and to connect to the management server so as to obtain the        profile,    -   the server for managing subscription data of an operator        designed to dispatch to the server the list of identification        values of the module and to provide the profile to the mobile        device comprising the security module.

The invention also relates to a computer program on a data medium andloadable into the memory of a computer, the program comprising codeportions for the execution of the steps of the method such as describedpreviously, when the program is executed on said computer.

The invention also pertains to a data medium in which the programhereinabove is recorded.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention will bebetter understood from the description and from the appended drawingsamong which:

FIG. 1 presents the steps of a method of anonymous identification of asecurity module, according to an exemplary embodiment;

FIG. 2 is a schematic representation of a discovery server, according toan exemplary embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The steps of a method of anonymous identification of a security module,according to an exemplary embodiment will now be described inconjunction with FIG. 1.

A mobile device 10, for example a mobile terminal or a tablet, equippedwith a security module 11 is designed to access the network of a mobileoperator MNO_(A) by means of a profile for accessing the networkgenerated by this operator for this module. More precisely, the profileis generated for this module by a subscription data management serverlinked with the operator. The profile comprises an application foraccess to the network and associated access data (one speaks of“credentials”), such as cryptographic keys and algorithms. The profilemakes it possible to authenticate the mobile device 10, more preciselythe security module 11 during access to the network of the operatorMNO_(A).

The security module 11 is typically an “eSIM” card (standing for“embedded Subscriber Identity Module”), or irremovable SIM card, of“eUICC” type (standing for “embedded Universal Integrated CircuitCard”). Such a security module is identified in a unique manner by meansof a module identifier “EID” (for “eUICC Identifier”), which constitutesa factory-defined and unmodifiable physical identifier of the card. Whena mobile device is equipped with a security module of eSIM card type,the user of the mobile device 10 can control, via an interface of themobile device or during a subscription in a shop of the operator, thedownloading of the profile into the security module 11. This mode ofoperation offers a certain flexibility during an initial subscription,or when there is a change of operator.

A discovery server 12, is an intermediate device situated in a datanetwork such as the Internet network. The discovery server 12 isdesigned to receive from operators, for example from the operatorMNO_(A), and more precisely from a server 13 for managing subscriptiondata of the operator, information that a profile for accessing thenetwork of the operator has been generated for a security module, forexample the module 11, and to record the address of the server 13 formanaging subscription data of the operator through which the profile canbe obtained in association with a list of anonymized identificationvalues which are specific to the security module 11 for which theprofile has been generated. The server 12 is also designed to receiverequests for address of a server for managing subscription data of anoperator originating from mobile devices, more precisely from securitymodules included in the mobile devices. To this end, the Internetaddress of the discovery server 12 is installed in the mobile device 10in the factory. As a variant, the address of the server 12 is installedin the security module 11 in the factory. The discovery server 12 isalso designed to provide, in response to a subscription data managementserver address request prompt emanating from the mobile device 10, theaddress of the server 13 for managing the subscription data of anoperator, here the operator MNO_(A). The server 13 for managing thesubscription data is designed to generate, following a subscription withthe operator MNO_(A), the profile for accessing the network of theoperator for the module 11. The security module 11 is designed toconnect, via the mobile device 10, to the server 13 for managing thesubscription data of the operator, after having obtained its addressfrom the discovery server 12, so as to download the profile foraccessing the network of the operator MNO_(A). The discovery server 12is independent of the network operators and receives the set ofsubscription data management server address request prompts originatingfrom the security modules, all operators inclusive.

It is assumed that in an initial step E0, a user, the owner of themobile device 10, takes out a new subscription with the operatorMNO_(A). The new subscription is for example an initial subscription,following the purchase of the mobile device 10, or, when the useralready possesses a subscription to a first operator, a subscriptionwith a second operator. For example, the user of the mobile device 10goes to an agency of the operator MNO_(A) and provides the operator withthe identifier EID of his security module 11. The identifier EID of themodule 11 is for example scanned on the mobile device 10 and transmittedto the server 13 for managing subscription data of the operator MNO_(A).

In a profile generating step E1, the server 13 for managing subscriptiondata of the operator MNO_(A) generates a profile for accessing thenetwork of the operator MNO_(A) for the mobile device 10, more preciselyfor the security module 11.

In a following step E2 of generating and dispatching a set ofidentification values, the server 13 for managing the subscription dataof the operator commands the generation of a set S of anonymizedidentification data specific to the security module 11. An anonymizedidentification datum specific to the security module 11 is computed onthe basis of the identifier EID of the security module 11 and of a date.The date varies in a timeslot lying between an initial date d_(s),representative of the date on which the subscription was taken out withthe operator MNO_(A) and a final date d_(f), representative of a date ofend of validity of the profile. The set S of anonymized identificationvalues thus comprises as many values as dates included in the slot. Thetimeslot lying between the initial date d_(s) and the final date d_(f)defines a time period during which it is possible to download theprofile onto the security module 13 once the subscription has been takenout. Indeed, it is considered that the profile is no longer valid if ithas not been downloaded onto the security module 11 beyond the finaldate d_(f). The granularity of the date is parametrizable. In anexemplary embodiment, the date is a calendar day; hours, minutes andseconds are not taken into account. The set S thus contains as manyidentification values as days lying between the initial date d_(s) andthe final date d_(f). The invention is not limited to this example.Thus, the date can correspond to a week, a month, or indeed to an hour.

In a first exemplary embodiment, the set S is generated as follows:

S={H(d_(s))^(EID′) mod p, H(d_(s)+1)^(EID′) mod p, H(d_(s)+2)^(EID′) modp, H(d_(s)+n)^(EID′) mod p}, where d_(s) represents the date on whichthe subscription was taken out, d_(s)+n the final date d_(f), EID′ anidentifier derived from EID, H a hash function and p a very large primenumber, for example 2048 bits in modular arithmetic. In this example,the date is a calendar day. The hash function H is for example thefunction SHA-3, or the function SHA-256. The invention is of course notlimited to these hash functions.

In an exemplary embodiment, the derived identifier EID′ is equal to theidentifier EID of the security module 11.

In another exemplary embodiment, the identifier EID′ is derived from EIDand comprises at least 160 bits. For example, the derived identifierEID′ is obtained by concatenating the identifier EID of the securitymodule 11 with a random value, shared with the security module 11, whichcomprises the number of bits required. The random value can be generatedby a security module manufacturer, or card maker, and previouslyinstalled in the security module 11 in the factory. In this case, in thecourse of the initial step E0, the identifier EID of the security module11 and the random value are provided to the operator. In this example,it is possible to prove the security of the computed anonymizedidentification values in the sense that, knowing H(d_(i))^(EID′) mod p,with d_(s)≤d_(i)≤d_(f), it is not possible to retrieve EID′. Statedotherwise, knowing an anonymized identification value, it is notpossible to retrieve the identifier EID′ of the associated securitymodule 11. Such a formula can indeed be associated with a known problemtermed the discrete logarithm problem, presumed to be difficult to solvein a reasonable time. Thus, the anonymity property is mathematicallyproven. Likewise, knowing two identification values H(d_(i))^(EID′1) modp and H(d₂)^(EID′2) mod p, it is not possible to ascertain whether theycorrespond to the same security module, stated otherwise whetherEID′₁=EID′₂. Solving such a problem would amount to solving theDiffie-Hellman decisional problem (or “DDH”, for “DecisionalDiffie-Hellman”), presumed to be difficult. Thus, it is not possible totrace a security module for which a first and a second profile have beengenerated, the first profile corresponding to a subscription to a firstoperator and the second profile to a subscription with a secondoperator. Indeed, it is not possible to correlate identification valuesets generated for one and the same security module by differentoperators. Thus the non-traceability property is mathematically proven.

In an exemplary embodiment, all the computations, including those of theanonymized identification values, are done over a cyclic sub-group of anelliptic curve where the Diffie-Hellman decisional problem is presumedto be difficult to solve. Indeed, elliptic curves guarantee a good levelof security with smaller modulos and sizes of keys. For example, amodulo p of 256 bits is sufficient.

The set S of anonymized identification values which is associated withthe operator MNO_(A) is transmitted to the discovery server 12 by thesubscription data management server 13 at the end of step E2.

The set S is received by the discovery server 12 in a step E3 ofreceiving and recording. The discovery server 12 stores the set S ofanonymized identification values in association with an address of amanagement server of the operator MNO_(A), for example the address ofthe subscription data management server 13.

Steps E0 to E3 are implemented during a phase of taking out asubscription by the user of the mobile device 10 with the operatorMNO_(A). At this juncture, the profile for accessing the network of theoperator is not yet installed on the security module 11 and does nottherefore allow the user of the mobile device 10 to access the mobilenetwork of the operator MNO_(A).

The subscription phase is followed by a profile request phase, intendedto allow the mobile device 10 to obtain the profile and to thus accessthe network of the operator MNO_(A). This profile request can be madeimmediately after taking out the subscription, or during the daysfollowing the subscription. In any event, the profile may not beobtained beyond its validity period fixed in this example at n days.

In a step E4 of dispatching a server address request prompt, the usercommands the dispatching, on the basis of an application of the mobiledevice 10, of an address request prompt in respect of a server formanaging subscription data of the operator MNO_(A) so as to obtain theaccess profile that the operator MNO_(A) has generated therefor duringthe subscription phase. The address request prompt is issued by themobile device 10, more precisely by the security module 11 identified byits identifier EID. It comprises a current anonymous identifier ID_(c),computed by the security module 11 as a function of its identifier EIDand of a current date d_(c). Note that with an aim of coordinationbetween the discovery server 12 and the mobile device 10, provision ismade for the mobile device 10 to dispatch a current date measured by themobile device 10 to the discovery server 12 so that the latter verifiesthat said date corresponds to a current date measured on the discoveryserver 12. This coordination makes it possible to ensure that the twoentities share the same current date and to alleviate a case where thecurrent date of the mobile device 10 would not yet be parametrized.Indeed, in this case the mobile device 10 would dispatch a default date,for example the 1 Jan. 1970, different from that of the server 12 andinappropriate for implementing comparisons of anonymized identificationvalues. In the example described here, the current anonymousidentification value ID_(c) of the module 11 is computed as follows:

ID _(c) =H(d _(c))^(EID′)mod p

Note that if the profile address request prompt is dispatched m daysafter the date d_(s) of subscription, then d_(c)=d_(s)+m.

The prompt for request of address of a server is received by thediscovery server 12 in a reception step E5.

In a following search step E6, the discovery server 12 searches for thecurrent anonymous identification value ID_(c) in the identificationvalue sets S that it has received from operators during the subscriptionphase. Note that this step is implemented only if the clocks of themobile device 10 and of the discovery server 12 are consistent.

In a first case where the current anonymous identification value ID_(c)is not found in any set of identification values (“nok” branch in FIG.1), then the method stops. This may be the case when the current dated_(c) is greater than the final date d_(f), indicating that the profileobtaining request for address was issued after the date of validity ofthe profile. This may be the case also when the user has not taken out asubscription: no profile has been generated by an operator for thesecurity module 11.

In a second case (“ok” branch in FIG. 1), the current anonymousidentification value ID_(c) figures in the list S of the anonymousidentification values which is stored by the discovery server 12. Thisindicates that the prompt for request of address of a subscription dataserver was issued by the security module 11 during the period ofvalidity of the profile and that this profile has been generated and isavailable for the security module 11.

In a response step E7, the discovery server 12 dispatches to thesecurity module 11 a response which comprises the address of the server13 for managing the subscription data of the operator MNO_(A) from whichthe module 11 can obtain the profile.

The response is received by the module 11 in a reception step E8.

In a following step E9 of obtaining the profile, the security module 11establishes a connection with the operator MNO_(A), more precisely withthe server 13 for managing the subscription data of the operator MON_(A)whose address figures in the response that it received in the course ofstep E8 so as to obtain the profile for accessing the network of theoperator MNO_(A). The access profile is downloaded onto the securitymodule 11. The user of the mobile device 10 can then access the mobilenetwork of the operator MNO_(A).

In an exemplary embodiment, it is verified that the server addressrequest prompt dispatched in the course of step E4 by the securitymodule 11 to the discovery server 12 is authentic. Stated otherwise, itis verified that the prompt emanates from an authentic module. To thisend, the security module 11 comprises a first secret key sk₁ which isspecific to the security module 11 and with which is associated a grouppublic key pk_(G), certified by a public key certificate, for example acertificate of type X509.v3. The secret key sk₁ is intended to be usedby the module 11 to sign the server address request prompt dispatched inthe course of step E4, by applying a group signature algorithm. Thegroup public key pk_(G) is intended to be used by the discovery server12 to verify the authenticity of the prompt. “Authentic prompt”signifies here that the prompt was generated by a security module thatpossesses one of the secret keys associated with the group public keypk_(G). Stated otherwise, the security module that signed the promptforms part of a group for which a certificate has been issued. The groupsignature mechanisms are assumed to be known. It is recalled here thatthe verification of a group signature by the discovery server 12 allowsit to be sure that the signature was generated by a member of the group;this verification does not however make it possible to identify themember of the group that has signed. In an exemplary embodiment, thegroup consists of the set of security modules that are manufactured byone and the same card maker. It is assumed that the first secret key sk₁is installed in the security module 11 in the factory. Thus, thesecurity module 11 is authenticated in an anonymous manner by thediscovery server 12.

In an exemplary embodiment, the group signature scheme is defined asfollows: consider three cyclic groups G₁, G₂ and G_(T) of prime order pand a bilinear coupling e: G₁×G₂→G_(T) of type 3. Let h and g be twogenerators of G₁ and o a generator of G₂. A manufacturer of securitymodules, or a card maker, plays the role of group manager and thereforepossesses a private key consisting of the triplet (x₀, x₁, x₂). Thepublic key pk_(G) associated with this private key is: (X₁=h^(x) ¹ modp, X₂=h^(x) ² mod p, O₀=o^(x) ^(o) mod p, O₁=o^(x) ¹ mod p, O₂=o^(x) ²mod p). The group manager installs in the security module 11 a groupcertificate σ=(u, u′=u^(x) ⁰ ^(+EID′x) ¹ ^(+sx) ² mod p), where u israndomly chosen and where s is a secret of the module 11.

To generate a group signature, the security module 11 firstly randomizesits group certificate by computing σ_(r)=(w=u^(r) mod p, w′=(u′)^(r) modp), where r is randomly chosen. Thereafter, it chooses three randomvalues z₁, z₂ and z₃ and then computes the following values:

c₁=w^(EID′) h^(z) ¹ mod p, c₂=w^(s)h^(z) ² mod p, c′=w′ g^(z3) mod p andV=g^(−z) ³ X₁ ^(z) ¹ X₂ ^(z) ² mod p

The group signature of the value Id_(c)=H(d_(c))^(EID′), is ω=(w, c₁,c₂, c′, V, π), where π is a proof of knowledge without disclosure ofknowledge “ZKPK” (standing for “Zero Knowledge Proof of Knowledge”)defined as follows: π=PoK [α, β, γ, λ, φ: c₁=w^(α)h^(γ) modp̂c₂=w^(β)hλ̂V=g^(−φ)X₁ ^(γ)X₂ ^(λ)̂Id_(c)=H(d_(c))^(α)] where α, β, γ, λand φ correspond to secret values known by the module 11 and knowledgeof which it wishes to prove. The notation π=PoK [α, β: statementconcerning α and β] is used to prove the knowledge of the secrets (α, β)which satisfy a certain statement without revealing anything more inregard to the secrets. By virtue of this conventional proof, thesecurity module 11 proves that it knows the secret values EID′, s, z₁,z₂ and z₃ without revealing anything more.

To verify the group signature, in particular that the module 11 doesindeed possess a valid group certificate and the associated secrets, thediscovery server 12 computes and firstly verifies that: e(w,O_(o))·e(c₁, O₁)·e(c₂, O₂)·e(c′, o)⁻¹=e(V, o). Thereafter, it verifiesthe validity of the proof π.

This group signature scheme is suitable for the limited computationalcapabilities of security modules of (e)SIM card type. Indeed, theproposed scheme is much less complex in terms of required computationalcapabilities and offers better performance in terms of computation timethan the conventional group signature schemes.

In another exemplary embodiment a secure channel is established betweenthe security module 11 and the server 13 for managing the subscriptiondata during step E9 of obtaining the profile. For example, the securitymodule has a second private key sk2 associated with a public key pk2certified by a public key certificate. The establishing of the securechannel between the server 13 for managing the subscription data and thesecurity module 11 is assumed to be known and is not detailed here.

In the example described here, the elements of the set S of anonymizedidentification values and the current identifier ID_(c) of the securitymodule 11 are computed by applying a hash function H to a date d and byraising the value obtained to the power of the derived identifier EID′of the module 11, modulo the prime number p. In another exemplaryembodiment, the set S is computed as follows:

S={H((EID″⊕ opad)∥H((EID″⊕ ipad)∥d _(s)))),H((EID″⊕ opad)∥H((EID″⊕ipad)∥d _(s)+1))), . . . ,H((EID″⊕ opad)∥H((EID″⊕ ipad)∥d _(s) +n)))},where

“∥” represents the concatenation operator, EID″ an identifier obtainedby adding ‘0's to EID’ so as to obtain an identifier of the size of ablock of the hash function H. Stated otherwise EID″=EID′∥ 00..00. ipadand opad are constructed by repeating respectively the bytes ‘0x36’ and‘0x5c’ until a block of the hash function H is obtained. The currentidentifier ID_(c) is computed in this case in the same manner for thecurrent date d_(c): ID_(c)=H((EID″ ⊕ opad)∥H((EID″⊕ ipad)∥d_(c)))).

This mode of computation exhibits the advantage of offering betterperformance in terms of computation time since the computations are lesscomplex than those implemented in the exemplary embodiment describedpreviously. Moreover, the security properties are satisfied: finding theidentifier EID′ associated with a security module and identifying thattwo anonymized identification values relate to one and the same securitymodule remains a problem which is difficult to solve.

A discovery server, according to an exemplary embodiment, will now bedescribed in conjunction with FIG. 2.

The discovery server 12 is a computing device, accessible from a datanetwork such as the Internet network. It comprises:

-   -   a processing unit or processor 121, or “CPU” (standing for        “Central Processing Unit”), intended for loading instructions        into memory, for executing them, for performing operations;    -   a set of memories, including a volatile memory 122, or “RAM”        (for “Random Access Memory”) used to execute code instructions,        to store variables, etc., and a storage memory 123 of “EEPROM”        type (standing for “Electrically Erasable Programmable Read Only        Memory”). In particular, the storage memory 123 is designed to        store a software module for anonymous identification of a        security module which comprises code instructions for        implementing the steps of the method of anonymous identification        of a security module such as described previously.

The discovery server also comprises:

-   -   a reception module 124, designed to receive from the security        module 11 and via the mobile device 10, a request for address of        the server for managing subscription data of the operator with        which a subscription has been taken. The request comprises a        current identification value ID_(c) of the module, computed on        the basis of the identifier of the security module 11 and of the        current date d_(c). The module 124 is designed to implement step        E5 of the method of anonymous identification of a module such as        described previously;    -   a search module 125, designed to search for the current        identification value ID_(c) received from the security module 11        in at least one set S of identification values. A set S of        identification values is received from an operator as soon as a        subscription is taken out with this operator. The set S        comprises for a given module, a plurality of anonymized        identification values, an identification value of the set being        computed as a function of the identifier of the module and of a        date, the date varying for the plurality of identification        values of the set between an initial date d_(s) and a final date        d_(f). The set S of anonymized identification values is stored        by the discovery server 12 in association with the address of a        server of the operator from which the profile can be obtained.        The search module 125 is designed to implement step E6 of the        method of anonymous identification of a security module such as        described previously;    -   a dispatching module 126, designed to dispatch to the security        module 11, the address of the server for managing subscription        data of the operator when the current identification value        ID_(c) figures in the set of identification values. The        dispatching module 126 is designed to implement step E7 of the        method described previously.

In an exemplary embodiment, the discovery server 12 also comprises:

-   -   a second reception module (not represented in FIG. 2), designed        to receive from the server for managing the subscription data of        the operator, the set S of identification values of the security        module and to associate this set with the address of the server        for managing the subscription data of the operator from which        the profile can be obtained. The second reception module is        designed to implement step E3 of the method of anonymous        identification of a security module such as described        previously.

The reception module 124, search module 125, dispatching module 126, andthe second reception module are preferably software modules comprisingsoftware instructions for implementing the steps of the method ofanonymous identification of a security module previously described.

The invention therefore also relates to:

-   -   a computer program comprising instructions for the        implementation of the method of anonymous identification of a        security module such as described previously when this program        is executed by a processor of the discovery server 12,    -   a readable recording medium on which the computer program        described hereinabove is recorded.

The invention also relates to an anonymous identification system whichcomprises a discovery server 12 such as described previously, a mobiledevice furnished with a security module 11 and a server 13 for managingsubscription data of the operator. The mobile device is designed todispatch to the discovery server 12 a request for address of a serverfor managing the subscription data of the operator, to receive inresponse the address of said management server, and to connect to themanagement server in order to obtain the profile. The server formanaging subscription data of the operator is designed to dispatch tothe discovery server 12 a list of anonymized identification values ofthe module that it has computed and to provide the mobile devicecomprising the security module with the profile that it has generatedfor the module during a subscription phase.

An exemplary embodiment of the invention remedies inadequacies/drawbacksof the prior art and/or to affords improvements thereto.

Although the present disclosure has been described with reference to oneor more examples, workers skilled in the art will recognize that changesmay be made in form and detail without departing from the scope of thedisclosure and/or the appended claims.

1. A method of anonymous identification of a security module by aserver, said method comprising: reception from the module of a requestfor address of a server for managing subscription data of an operator,said request comprising a current identification value of the module,said current identification value being dependent on an identifier ofthe module and a current date, searching for the current identificationvalue in at least one set of identification values, said set beingassociated with an operator and comprising for a given module, aplurality of identification values, an identification value beingcomputed as a function of the identifier of the module and of a date,the date varying for the plurality of identification values of the setbetween an initial date and a final date, dispatching to the securitymodule of the subscription data management server address associatedwith the operator when the current identification value figures in theset of identification values.
 2. The method as claimed in claim 1comprising in a prior subscription phase: reception, from the server formanaging the subscription data of the operator of the set of theidentification values of the module, said set being associated by theserver with the operator.
 3. The method as claimed in claim 1,furthermore comprising: application of a group signature algorithmparametrized by a secret key specific to the security module to therequest for address of the subscription data management server of theoperator, verification of the signature of the request for address bythe server by using a group public key, associated by a public keycertificate with a set of modules comprising at least said securitymodule.
 4. The method as claimed in claim 1, in which the servercomputes an identification value by applying a hash function to a dateand by raising the value obtained to the power of an identifier derivedfrom the identifier of the module.
 5. The method as claimed in claim 4,in which the derived identifier comprises at least 160 bits.
 6. Themethod as claimed in claim 5, in which the derived identifier isobtained by concatenating the identifier of the module with a randomvalue.
 7. The method as claimed in claim 1, in which an identificationvalue is computed by applying a hash function to the concatenation of afirst identifier derived from the identifier of the module and of thehash of the concatenation of a second identifier derived from theidentifier of the module and the date.
 8. A server of a network designedto anonymously identify a security module, said server comprising: aprocessor; and a non-transitory computer-readable medium comprisinginstructions stored thereon, which when executed by the processorconfigure the server to perform acts comprising: receiving from themodule, a request for address of a server for managing subscription dataof an operator, said request comprising a current identification valueof the module, said current identification value being dependent on anidentifier of the module and a current date, searching for the currentidentification value received from the module in at least one set ofidentification values, said set being associated with an operator andcomprising for a given module, a plurality of identification values, anidentification value being computed as a function of the identifier ofthe module and of a date, the date varying for the plurality ofidentification values of the set between an initial date and a finaldate, dispatching to the security module the address of the profilesdata management server associated with the operator when the currentidentification value figures in the set of identification values.
 9. Asystem for obtaining a network access profile, comprising: the server asclaimed in claim 8, and a mobile device comprising the security module(11), said mobile device being designed to dispatch to the server arequest for address of a server for managing the subscription data ofthe operator, to receive in response the address of said managementserver, and to connect to the management server so as to obtain theprofile, the server for managing subscription data of an operatordesigned to dispatch to the server the list of identification values ofthe module and to provide the profile to the mobile device comprisingthe security module.
 10. (canceled)
 11. A non-transitorycomputer-readable data medium comprising program code instructionsrecorded thereon, which when executed by a processor of a serverconfigure the server to anonymously identify a security module byperforming the following acts: receiving from the module of a requestfor address of a server for managing subscription data of an operator,said request comprising a current identification value of the module,said current identification value being dependent on an identifier ofthe module and a current date, searching for the current identificationvalue in at least one set of identification values, said set beingassociated with an operator and comprising for a given module, aplurality of identification values, an identification value beingcomputed as a function of the identifier of the module and of a date,the date varying for the plurality of identification values of the setbetween an initial date and a final date, dispatching to the securitymodule of the subscription data management server address associatedwith the operator when the current identification value figures in theset of identification values.